Built-in dictionary functions commonly used in python

Source: Internet
Author: User

1. len (mapping) returns the ing length (number of key-value pairs)

2. hash (obj) returns the hash value of obj.

>>> myDict = {'name':'earth', 'port':'80'}>>> len(myDict)2>>> hash('name')15034981

3. dict. copy () returns a copy of the Dictionary (light copy ).

>>> myDict = {'name':'earth', 'port':'80'}>>> yourDict = myDict.copy()>>> yourDict{'name': 'earth', 'port': '80'}>>> id(myDict)41816664L>>> id(yourDict)41819544L

4. dict. clear () deletes all elements in the dictionary.

>>> myDict.clear()>>> myDict{}

5. dict. fromkeys (seq, val = None)

Create and return a new dictionary. Use the elements in seq as the dictionary key, and val as the initial values corresponding to all keys in the dictionary (if this value is not provided, the default value is None ).

>>> seq = ['name', 'port']>>> myDict.fromkeys(seq){'name': None, 'port': None}

6. dict. get (key)

Return the value corresponding to the key in the dictionary dict. If the key does not exist in the dictionary, the default value is returned (note that the default value of the parameter default is None ).

>>> myDict = {'name':'earth', 'port':'80'}>>> myDict.get('name')'earth'>>> print myDict.get('home')None

7. dict. items () returns a list of key-value pairs in the dictionary.

>>> myDict.items()[('name', 'earth'), ('port', '80')]

8. dict. keys () returns a list containing the dictionary's middle keys.

9. dict. values () returns a list containing all values in the dictionary.

>>> myDict.keys()['name', 'port']>>> myDict.values()['earth', '80']

10. dict. iter ()
Methods iteritems (), iterkeys (), and itervalues () are the same as their non-iterative methods. The difference is that they return an iterator instead of a list.

11. dict. pop (key [, default])
Similar to the get () method, if the key in the dictionary exists, delete it and return the dict [key]. If the key does not exist and no default value is given, a KeyError exception is thrown.

>>> myDict.pop('port')'80'>>> myDict{'name': 'earth'}>>> myDict.pop('port', 'No such key!')'No such key!'

12. dict. setdefault (key, default = None)
Similar to the method set (), if the dictionary does not contain a key, the value is assigned by dict [key] = default.

>>> myDict.setdefault('port', '8080')'8080'>>> myDict{'name': 'earth', 'port': '8080'}

13. dict. update (dict2) adds the key-value pairs of the dictionary dict2 to the dictionary dict.

>>> yourDict = {'language':'Python'}>>> yourDict{'language': 'Python'}>>> myDict.update(yourDict)>>> myDict{'name': 'earth', 'language': 'Python', 'port': '8080'}

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